scholarly journals Extremely Southward Migration of the Antarctic Circumpolar Current During the Last Interglacial

2021 ◽  
Author(s):  
Lijuan Lu ◽  
Xufeng Zheng ◽  
Zhong Chen ◽  
Michael Weber ◽  
Victoria Peck ◽  
...  
Keyword(s):  
Grain Size ◽  
Antarctic Circumpolar Current ◽  
Meridional Overturning Circulation ◽  
Apparent Difference ◽  
Last Interglacial ◽  
The Holocene ◽  
Mean Grain Size ◽  
Circumpolar Current ◽  
Mis 5E ◽  
The Antarctic

Abstract The Antarctic Circumpolar Current (ACC) acts as a critical component to regulate the global thermohaline circulation and climate. However, active debate remains about the relative strength of ACC during current/past warm periods and underlying driving mechanisms. Here, we present sortable silt mean grain size records from the Scotia Sea to infer the ACC strength over the past 160 ka. The 22-ka cycles of sortable silt mean grain size suggest that the precession-driven contraction/expansion of Subtropical Jet dominates the migration of ACC fronts, and thus ACC speed and potential Atlantic Meridional Overturning Circulation stability. We find that the bottom flow speed during MIS 5e was over three times faster than the Holocene, with no apparent difference in ACC speed between the Holocene and the Last Glacial Maximum. We suggest that a southward shift of oceanic fronts of ~5° could cause the additional speed-up of ACC during MIS 5e. This could induce warmer water flowing in the ACC to approach and melt the Antarctica continental ice shelves, with corresponding effects on global sea level and the global climate.

Upper-Ocean Eddy Heat Flux across the Antarctic Circumpolar Current in Drake Passage from Observations: Time-Mean and Seasonal Variability

2020 ◽  
Vol 50 (9) ◽  
pp. 2507-2527
Author(s):  
Manuel O. Gutierrez-Villanueva ◽  
Teresa K. Chereskin ◽  
Janet Sprintall
Keyword(s):  
Heat Flux ◽  
Antarctic Circumpolar Current ◽  
Drake Passage ◽  
Polar Front ◽  
Meridional Overturning Circulation ◽  
Time Varying ◽  
Eddy Heat Flux ◽  
Meridional Overturning ◽  
Circumpolar Current ◽  
The Antarctic

AbstractEddy heat flux plays a fundamental role in the Southern Ocean meridional overturning circulation, providing the only mechanism for poleward heat transport above the topography and below the Ekman layer at the latitudes of Drake Passage. Models and observations identify Drake Passage as one of a handful of hot spots in the Southern Ocean where eddy heat transport across the Antarctic Circumpolar Current (ACC) is enhanced. Quantifying this transport, however, together with its spatial distribution and temporal variability, remains an open question. This study quantifies eddy heat flux as a function of ACC streamlines using a unique 20-yr time series of upper-ocean temperature and velocity transects with unprecedented horizontal resolution. Eddy heat flux is calculated using both time-mean and time-varying streamlines to isolate the dynamically important across-ACC heat flux component. The time-varying streamlines provide the best estimate of the across-ACC component because they track the shifting and meandering of the ACC fronts. The depth-integrated (0–900 m) across-stream eddy heat flux is maximum poleward in the south flank of the Subantarctic Front (−0.10 ± 0.05 GW m−1) and decreases toward the south, becoming statistically insignificant in the Polar Front, indicating heat convergence south of the Subantarctic Front. The time series provides an uncommon opportunity to explore the seasonal cycle of eddy heat flux. Poleward eddy heat flux in the Polar Front Zone is enhanced during austral autumn–winter, suggesting a seasonal variation in eddy-driven upwelling and thus the meridional overturning circulation.

scholarly journals Magnetic properties of Upper Quaternary sediments from the Scotia Sea, Antarctica

2001 ◽  
Vol 13 (1) ◽  
pp. 61-66
Author(s):  
Norman Hamilton ◽  
Carol J. Pudsey
Keyword(s):  
Grain Size ◽  
Magnetic Properties ◽  
Antarctic Circumpolar Current ◽  
Quaternary Sediments ◽  
Scotia Sea ◽  
Fine Grained ◽  
Core Site ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Size Data

Magnetic properties of bulk sediment samples taken from three cores from the Scotia Sea, Antarctica were determined using a fully-automated variable field translation balance. Fine-grained detrital magnetite is identified as the principal carrier of remanence in these Upper Quaternary sediments which were deposited under the influence of the Antarctic Circumpolar Current. Inferred magnetite grain-size is consistent with published bulk grain-size data for these cores. Pseudo-single domain grains characterize Holocene samples, and larger, multi-domain grains occur in glacial samples from two of the cores, whereas samples from the northernmost core site show dominantly multi-domain behaviour.

scholarly journals Reshaping the Antarctic Circumpolar Current via Antarctic Bottom Water Export

2017 ◽  
Vol 47 (10) ◽  
pp. 2577-2601 ◽  
Author(s):  
Andrew L. Stewart ◽  
Andrew McC. Hogg
Keyword(s):  
Antarctic Circumpolar Current ◽  
Bottom Water ◽  
Channel Model ◽  
Meridional Overturning Circulation ◽  
Sea Surface ◽  
Momentum Balance ◽  
Antarctic Bottom Water ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Zonal Momentum

AbstractZonal momentum input into the Antarctic Circumpolar Current (ACC) by westerly winds is ultimately removed via topographic form stress induced by large bathymetric features that obstruct the path of the current. These bathymetric features also support the export of Antarctic Bottom Water (AABW) across the ACC via deep, geostrophically balanced, northward flows. These deep geostrophic currents modify the topographic form stress, implying that changes in AABW export will alter the ocean bottom pressure and require a rearrangement of the ACC in order to preserve its zonal momentum balance. A conceptual model of the ACC momentum balance is used to derive a relationship between the volume export of AABW and the shape of the sea surface across the ACC’s standing meanders. This prediction is tested using an idealized eddy-resolving ACC/Antarctic shelf channel model that includes both the upper and lower cells of the Southern Ocean meridional overturning circulation, using two different topographic configurations to obstruct the flow of the ACC. Eliminating AABW production leads to a shallowing of the sea surface elevation within the standing meander. To quantify this response, the authors introduce the “surface-induced topographic form stress,” the topographic form stress that would result from the shape of the sea surface if the ocean were barotropic. Eliminating AABW production also reduces the magnitude of the eddy kinetic energy generated downstream of the meander and the surface speed of the ACC within the meander. These findings raise the possibility that ongoing changes in AABW export may be detectable via satellite altimetry.

scholarly journals Orbital- and millennial-scale variability of the Antarctic Circumpolar Current over the past 140,000 years

2020 ◽  
Author(s):  
Shuzhuang Wu ◽  
Lester Lembke-Jene ◽  
Frank Lamy ◽  
Helge Arz ◽  
Norbert Nowaczyk ◽  
...  
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
Antarctic Circumpolar Current ◽  
Cold Water ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
The Past ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Millennial Scale

Abstract The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage over the past 140,000 years, based on grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with reduced ACC intensity during glacials and a more vigorous circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We hypothesize that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations regulated Pacific-Atlantic water exchange via the “cold water route” and affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

scholarly journals Diapycnal Mixing in the Antarctic Circumpolar Current

2011 ◽  
Vol 41 (1) ◽  
pp. 241-246 ◽  
Author(s):  
J. R. Ledwell ◽  
L. C. St. Laurent ◽  
J. B. Girton ◽  
J. M. Toole
Keyword(s):  
Antarctic Circumpolar Current ◽  
Austral Summer ◽  
Drake Passage ◽  
Meridional Overturning Circulation ◽  
Velocity Shear ◽  
Reference Spectrum ◽  
Diapycnal Mixing ◽  
Diapycnal Diffusivity ◽  
Circumpolar Current ◽  
The Antarctic

Abstract The vertical dispersion of a tracer released on a density surface near 1500-m depth in the Antarctic Circumpolar Current west of Drake Passage indicates that the diapycnal diffusivity, averaged over 1 yr and over tens of thousands of square kilometers, is (1.3 ± 0.2) × 10−5 m2 s−1. Diapycnal diffusivity estimated from turbulent kinetic energy dissipation measurements about the area occupied by the tracer in austral summer 2010 was somewhat less, but still within a factor of 2, at (0.75 ± 0.07) × 10−5 m2 s−1. Turbulent diapycnal mixing of this intensity is characteristic of the midlatitude ocean interior, where the energy for mixing is believed to derive from internal wave breaking. Indeed, despite the frequent and intense atmospheric forcing experienced by the Southern Ocean, the amplitude of finescale velocity shear sampled about the tracer was similar to background amplitudes in the midlatitude ocean, with levels elevated to only 20%–50% above the Garrett–Munk reference spectrum. These results add to a long line of evidence that diapycnal mixing in the interior middepth ocean is weak and is likely too small to dictate the middepth meridional overturning circulation of the ocean.

scholarly journals Inferring the Pattern of the Oceanic Meridional Transport from the Air–Sea Density Flux

2008 ◽  
Vol 38 (12) ◽  
pp. 2722-2738 ◽  
Author(s):  
Timour Radko ◽  
Igor Kamenkovich ◽  
Pierre-Yves Dare
Keyword(s):  
Antarctic Circumpolar Current ◽  
Water Mass ◽  
Meridional Overturning Circulation ◽  
Diagnostic Model ◽  
Global Budget ◽  
Meridional Transport ◽  
Meridional Overturning ◽  
The Difference ◽  
Circumpolar Current ◽  
The Antarctic

Abstract An extension of Walin’s water mass transformation analysis is proposed that would make it possible to assess the strength of the adiabatic along-isopycnal component of the meridional overturning circulation (MOC). It is hypothesized that the substantial fraction of the adiabatic MOC component can be attributed to the difference in subduction rates at the northern and southern outcrops of each density layer—the “push–pull” mechanism. The GCM-generated data are examined and it is shown that the push–pull mode accounts for approximately two-thirds of the isopycnal water mass transport in the global budget and dominates the Atlantic transport. Much of the difference between the actual interhemispheric flux and the push–pull mode can be ascribed to the influence of the Antarctic Circumpolar Current, characterized by the elevated (at least in the GCM) values of the diapycnal transport. When the diagnostic model is applied to observations, it is discovered that the reconstructed MOC is consistent, in terms of the magnitude and sense of overturning, with earlier observational and modeling studies. The findings support the notion that the dynamics of the meridional overturning are largely controlled by the adiabatic processes—time-mean and eddy-induced advection of buoyancy.

scholarly journals Nonlinear Differential Equations Modeling the Antarctic Circumpolar Current

2021 ◽  
Vol 23 (4) ◽  
Author(s):  
Jifeng Chu ◽  
Kateryna Marynets
Keyword(s):  
Fixed Point ◽  
Differential Equations ◽  
Boundary Conditions ◽  
Topological Degree ◽  
Antarctic Circumpolar Current ◽  
Fixed Point Theorems ◽  
Nonlinear Differential Equations ◽  
Existence Results ◽  
Circumpolar Current ◽  
The Antarctic

AbstractThe aim of this paper is to study one class of nonlinear differential equations, which model the Antarctic circumpolar current. We prove the existence results for such equations related to the geophysical relevant boundary conditions. First, based on the weighted eigenvalues and the theory of topological degree, we study the semilinear case. Secondly, the existence results for the sublinear and superlinear cases are proved by fixed point theorems.

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